| For the investigation of the mechanism of the yield point suppression behavior of pure iron due to electrolytically charged hydrogen, tensile tests of the pure iron specimens were conducted at the temperature and strain rate in the ranges of 285∼318 K and 3.3 ×10＾(-5)∼3.3×10^(-2), respectively. To charge hydrogen into the specimen the current density was maintained in the range of 10∼300A/㎡. Stress relaxation tests and density measurement were also conducted with or without hydrogen changing. Specimen density was measured to be significantly reduced after hydrogen charging. In the case of hydrogen charged specimen, almost all the stress was relaxed, on the other hand, for the specimen without hydrogen the relaxed stress was very small. Yield point phenomenon was disappeared and the yield stress was significant1y reduced by the charged hydrogen. All the experimental results imply that the charged hydrogen forms cavities and these cavities expand in size by the tensile stress. Since there are quite a few number of cavities formed by the hydrogen, at the beginning of the tensile, all the cavities begin to expand to en-large the specimen length. At this stage the specimen begin deform around the cavities which are uniformly distributed. Therefore, one may see the reduced yield stress and may not observe the yield point phenomenon. |
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